Finding the Key to CIGS PV Reliability

by Joseph McCabe, PE

This past week there was a photovoltaic
(PV) workshop that probably wasn't on your radar. It was held at the
National Renewable Energy Laboratory (NREL) and is called the PV
Module Reliability Workshop (PVMRW). This is where the nerds of the
PV industry get together to discuss the factors that influence how
long a PV module will last and other factors which might influence
the long-term performance of a PV system. It wasn't on your radar
because it is not something that influences big business. Or is it?

If you track the PV industry it is more
likely that you heard about the February 16th Photon CIS conference
in San Francisco where high level people were discussing their
company capacities and expected CIS efficiencies. But at the PVMRW
meeting, held at the same time, people were discussing the challenges
with copper indium gallium and (di)selenide PV (CIGS), which is very
similar to CIS. CIGS has the promise of low cost manufacturing with
high efficiencies. However many companies are taking quite a long
time to develop large markets. CIGS products deposited on glass, like
Solar Frontiers (100% subsidiary of Showa Shell [Tokyo:5002]), have
had many years of advancements leading to the February 15th
announcement indicating commercial production at their newest plant
located in Kunitomi Japan.

The Promise of CIGS

CIGS holds the promise of low cost
production and of being packaged in a flexible module. This month’s
Department of Energy (DOE) SunShot
Initiative announcement hopes to reduce PV
systems costs by about 75 percent to roughly $1 per watt; flexible
CIGS PV modules can provide a large system level price reduction
towards this DOE goal. NREL specifically indicated the system level
cost reductions could be from $0.17 to $0.94 per watt savings using
flexible PV modules instead of traditional rigid glass.

The Hunt for the Culprit

The high efficiency, flexible PV module
has been hampered by apparent susceptibility to moisture of the CIGS
technology. Potential culprits range from the packaging of the
modules that allow for moisture to enter into the PV cells to
transparent conductive oxides (TCO). TCO are one of the layers in the
CIGS thin film PV module.

At PVMRW companies like Dow Corning,
DuPont, Saint-Gobain, Mitsubishi Plastics, and 3M were presenting how
their materials can protect the PV product, specifically CIGS
susceptibility to moisture. If the culprit causing the
susceptibility to moisture inherent in today's CIGS technologies is
the TCO, as NREL suggests, these expensive and unproven packaging
solutions might not be needed.

Various CIGS companies provided
reliability perspectives at the PVMRW. SoloPower, which just
announced a conditional commitment for a $197M loan guarantee from
the DOE for a new facility in Oregon, presented the effects of light
soaking on shunts in their CIGS. Solarion compared reliability of
their CIGS in a glass-glass encapsulation to a flexible
encapsulation. Ascent
Solar
(ASTI) presented highly accelerated weathering
of CIGS and Nanosolar presented their design for reliability on
keeping the water out of CIGS. Companies like ADCO adhesives were
supplying reliability information on edge seals and other building
integrated PV (BIPV) adhesive attachment solutions appropriate for
flexible CIGS.

One company's presentation was quite
revealing. Sunpower
(SPWRA) had quantified and presented various
system failures to help understand reliability from their extensive
historical field experience. SunPower's acquisition of PowerLight
enabled them to compare various manufactures’ products over a
number of years of performance data. This sharing of system failure
data is indicative of the spirit of this unique PVMRW meeting. Our
industry is learning from each others failures so that the industry
as a whole will prosper. Just a note, SunPower’s modules were not
necessarily those included in the system failures, but other
manufactures modules.

Reliability is Location-Specific

For the first time I was hearing
multiple discussions for location specific reliability evaluations.
All modules are currently required to pass a set of tests that help
build confidence in the safety and potential performance of the PV
over time. However, there is not necessarily a correlation of those
tests and the actual longevity of the PV product. It has only been
assumed that these tests can represent a high probability of
long-term performance. The tests reflect a general understanding of
failure mechanisms for a relatively hot-humid location. New location
specific reliability testing can open up hot dry markets for specific
PV technologies, and can help to guarantee performance of PV products
that might perform better in cold or humid climates. NREL’s Rommel
Noufi
suggested looking at today’s highways for what our PV industry
might look like in the future. What he meant is that the highways are
full of various manufactures and models of transportation solutions,
and similarly, there will be many PV solutions for various locations
and purposes in the future.

There were three tracks at the PVMRW;
crystalline silicon, concentrating PV and thin film. CIGS discussions
dominated the thin film track possibly due to the high interest in
long term performance opportunities. Kudos has to go to NREL and the
DOE for supporting this annual PVMRW workshop. And thanks should go
out to the nerds of the industry who have worked for many years to
build the current state of reliability in the PV industry. Over the
past few decades it is these groups of people that have enabled PV
systems to build the confidence in the PV market place that enables
more than 20 years of reliable system performance.

DISCLOSURE:
No
positions.

Joseph
McCabe
is a solar industry nerd with over 20 years in the business.
He is an American Solar Energy Society Fellow, a Professional
Engineer, and is internationally recognized as an expert in thin film
PV, BIPV and Photovoltaic/Thermal solar industry activities. Joe is a
Contributing Editor to altenergystocks and can be reached at energy
[no space] ideas at gmail dotcom.